The present invention pertains to a type of tool which will be referred to herein as "dual packer apparatus," and is more commonly referred to as a "straddle packer." This type of apparatus generally includes two packers run in longitudinally spaced positions on a common operating string. After the apparatus has been run into a well bore, the packers may be set to separate three consecutive zones of the well from one another. Such isolation may be required to permit the performance of testing and other operations on various of these zones individually. It is generally desirable that the apparatus permit successive operations of this sort upon different zones without removal and re-running of the operating string and with a minimum of manipulation of the tool.
At least one other straddle packer type apparatus is known to be currently available. One major problem with this existing apparatus is difficulty of assembly. Because of the size of the apparatus, it is impractical, if not impossible, to deliver it to the well site in assembled condition. The tool includes both inner and outer parts. Each inner part is pre-positioned in its respective outer part so that as the tool is assembled at the well site, the inner and outer parts must be separately supported during the assembly process. This in turn requires the use of special, complicated elevators, and is generally a time-consuming, tedious and troublesome process.
Further complicating the procedure is the fact that a sensor line, e.g. for sensing temperature and/or pressure, is usually installed within the straddle packer apparatus, and extending along its length. Such a sensor line typically represents still a third set of parts which must be assembled and installed in the context of the already complicated assembly procedure described above.